What's causing fuel imbalance on cylinder banks

[slazisme]

Hi guys, maybe someone can help with this issue I'm having. Running the LS fitech 70050 with dual widebands mounted same distance on each bank from header(mid length) collector and I am seeing roughly a 20% correction fuel imbalance between banks.
The drivers side cylinder bank is running richer than the passenger side. Engine is iron LS3, Comp 222/224 dur. .565/.568 lift, 10.2 comp. LS3 intake with 42 lb injectors. 92mm throttle body.

I know before I get comments about this system it was purchased back in Nov. /2017 before Holley came out with their Terminator stuff.

Any ideas what could be the issue........exhaust leak? injector(s), bad o2 sensor? Thanks.

# 2 cyl. #3 cyl.

[68Formula]

A bank to bank issue is most often an exhaust leak. Start there. Bad O2 sensors is second most common. That much of a delta I would not expect to be from injectors unless your getting a complete misfire on a cylinder. Also check for intake leaks on the lean side.

[Vimes]

On the O2 sensors, while you're checking for exhaust leaks, swap sensors side to side and clear your program. If you see the same imbalance the other way, it confirms the O2 as the problem. If you do find a leak, it won't matter what side has what sensor, so you can just leave them swapped.

[slazisme]

Thanks to both of you for your responses, when I had the car up on a hoist getting a bunch of front end components changed there was no visible leak showing any puffs of carbon staining anywhere.....header flange, v-band area, o2 sensor areas clean.
I will swap out the o2 sensors and see if the other bank reads rich that could point to a sensor problem. Also going to take out the spark plugs on both banks and see if there is a visible difference on a specific(bad) cylinder that could be the cause of computer enriching a bank.

[slazisme]

Took the plugs out for an inspection and the pics tell me that #1 cylinder plug looks pretty clean with not really any signs of carbon, the rest look pretty much the same. If you guys think differently chime in.

#1-3-5-7 plugs


#1


#8-6-4-2

I'm going to get a new plug for #1 and change # 1 injector and see if this cure's the enriching drivers bank otherwise I'm open to suggestions.

[68Formula]

When are you getting the 20% correction? Idle only? Cruising? Tip in acceleration? WOT? All of the above? Some, but not others?

[slazisme]

It seems to be adding fuel in the 1300-1800 range mostly from my last log. I'll post the log I did on June 16th for you to look at. I'm coming from a SBC platform and learning fuel injection. Any help is really appreciated. My tuning guy is familiar with Terminator and Fast stuff but has helped me a bunch up to now.

It seems I can't post my most recent log file, if you want to send me a PM with email address I'll send it to you for analysis. If you don't want to I understand but thanks for helping.
I'm thinking maybe the injector isn't flowing like the others? cause the plug looks clean, maybe the plug? wire? At this point I just want to get things balanced. The car otherwise runs fine.
Here's a video from when I fired it up last November.

[dhutton]

I had a similar experience on a recent LT based build with the factory ECM. One bank was going rich when I looked at the fuel trims. There were no codes. I replaced the O2 sensor in that bank but at the same time I swapped the plugs side to side. After a short while the other bank fuel trims went rich. I replaced the plugs and it has run great ever since. Never understood why no codes were generated.

Don

[68Formula]

That's a good point DH. The LTFTs will take a while to catch up to the STFT corrections if you try a O2 bank to bank swap.

[slazisme]

Don, 68 formula thanks.........I picked up another spark plug and will first try the new one in the #1 spot and see if it make a difference in the next few days. Today was a hot one at 98 degrees here, I know that the southwest has had a heat wave for about a week now........hope everyone is coping well.
I've got another o2 sensor and will use it if I have to but the 2 that are on the car are fairly new so lets see if the drivers side fuel trims get adjusted down or keep getting enriched.

[Hotwire]

As stated above, I would swap the installed o2 sensors and see if the fueling follows the sensors or stays w/ the bank. That will help to eliminate questions and guessing as to what the problem is.

You could also pull the fuel rail, prime the fuel pressure, and look to see if any injectors are leaking. It's all a process of elimination.

[slazisme]

A little update as I believe things are okay now. Started off by getting a new spark plug for #1 cylinder, got a new 42Lb injector, swapped around D510c coils and plug wires to see if it would follow or make any difference, then swapped o2 sensors to see if the problem would follow the bank. All of these remedies didn't alter things.
As worst case scenario I was starting to think maybe coolant was seeping into the the #1 cylinder and steam cleaning the plug and dreading the fact that the head would have to come off for inspection, or possibly a faulty ecm.

Last week I changed the coil harness and added a ground strap to the drivers side cylinder head. Well when I first started it up after this the fuel trims on the drivers side started showing 20-15% minus upon startup. Don't know which one helped, my tuner thinks it was the ground. Boy was I happy to see #1 plug start to get carbon fouled. So far so good just have to adjust the fuel table on the upper end as the computer started adding fuel at 5806 rpm to the tune of 11.7% after I downloaded a fuel log last Friday. Thanks for all the suggestions.

[Beamie]

I had a similar experience on a recent LT based build with the factory ECM. One bank was going rich when I looked at the fuel trims. There were no codes. I replaced the O2 sensor in that bank but at the same time I swapped the plugs side to side. After a short while the other bank fuel trims went rich. I replaced the plugs and it has run great ever since. Never understood why no codes were generated.

Don

I have this issue with my 2k6 Pontiac Grand Prix GXP 5.3L with Bank 1 running rich. I resolved most of the vacuum leaks. I have to see if I a vacuum leak is at the injector or bad upstream O2 sensor.